1. Field of the Invention
The present invention relates to a method and a system for controlling web formation in the forming section of a paper machine.
2. Discussion of Background Information
The traditional way of measuring drainage in the forming section is to use a backscatter gamma gauge. As this instrument measures the fabric weight, fiber weight and water weight, it is necessary to manually determine the thinstock consistencies between the machine direction measurement points in order to calculate the water weight difference. The main drawback with such a device relates to the portability of its ionizing gamma radiation source within mills and across national borders. Often this sensor cannot be transported in an aircraft.
Alternative measurement techniques have been used by which water can be measured without using an ionizing source. In particular, ultrasonic sensors have been used. However, such an ultrasonic measurement may not work beyond the dryer line and cannot work in situations where the stock contains over 0.75% air content on a volumetric basis. As a consequence, this technique is not considered acceptable.
It is therefore an object of the present invention to provide an improved method and an improved system of the kind initially mentioned with which the above-mentioned problems can be eliminated.